Modulation control system



Aug. 13, 1935. L. H. PADDLE 2,911,499

MODULATION CONTROL SYSTEM Filed June 26, 1953 4 Sheefs-Sheei 1 Aug. 13, 1935.

L. H. PADDLE MODULATI ON CONTROL SYSTEM Filed June 26, 1933 4 Sheets-Sheet 2 Invader I my- Aug, 13, 1935. L. H. PADDLE 2,011,499

MODULATION CONTROL SYSTEM Filed June 26, 1953 4 Sheets-Sheet z Imago)" Aug. 13, 1935. L. H. PADDLE 2,011,499

MODULATION CONTROL SYSTEM I Filed June 26, 1953 4 Sheets-Sheet 4 f-rw-enibr Z 5/ WA Or Patented Aug. 13, 1935 UNITED STATES PATENTOFFICE H V V I Q 2,011,499 j' 1 f A MODULATION CONTROL SYSTEM 7 Leslie Harold Paddle, Chiswick, London, England 7 Application June 26, 1933; Serial No. 677,757 In Great Britain June'29, 1932 7 Claims. (01. 179-171 I This invention relates to the. control of fiveelectrodethermionic valves or pentodes, that is valvesv having, in addition to the anode, cathodev and control grid, a grid near the anode, con- I: nected to a point of low potential on the cathode to prevent secondary emission from'the anode, and an auxiliary grid between the other two grids, adapted to be connected to-a source of positive potential.

I have found that variations in the potential appliedto the auxiliary grid, without substantially changing the anode-cathode impedance, eilect corresponding variations in the 'static characteristic curve of the valve in such a way that 1 reduction of said potential efiects a reduction of the amount of the grid swing which the valve is capable of relaying until a point is reached at which said valve-is rendered completely nontransmissive, whereasincrease of said potential efiects an increase of said amount until it attains a maximum when the potential of the auxiliary grid is equal to that of the anode.

' The object of the invention is the provision of an improved method of controlling the output from such valves, by which method it will-be possible inter-alia-for either a transmitter or a receiver to be made quiescent, that is to .say,

adaptedv automatically to transmit or receive the carrier waves only when a signal is in existence to be transmitted or received; 1

The invention consists broadly in the arrangement that the output from the, valve is controlled through variation in the potential applied to'the auxiliary grid, such variation being eifected automatically by some desired signal.

, This potential variation may be effected auto matically inresponse to the signal by which the carrier wave is to be modulated (when the pentode. is employed in a transmitter) or by the (when said pentode is employed in a receiver) in sucha way that when there is no signal the auxiliary grid potential. is reduced to thepoint at which the valveis nontransmitting, and when'there is a' signal said auxiliary grid potential is increased in proportion. to the amplitude of said signal in such a way that the amount of grid swing which the valve is capable of transmitting is always sunlcient to-comprise the range through which the :carrier waveis modulated.-

In thejcase both of the transmitter and the receiver this potential variation may be effected through the medium of an anode bend detector operated by the signal.

In order that the invention may be the more transmitter.

' load or output circuit.

clearly understooda number of circuits in ace cordance therewith will now be described'reie'rence being made to the accompanying drawings Wherein:-'-'.. v r Figure 1 illustrates a circuit in which the pentode is employed as an amplifier in a radio receiving set, L

'Figure 2. illustrates a slightly diiierent circuit toithat ofliigurefl. I of .HFigure'S illustrates a circuit .in which the pentode is employed as the modulator in a-trans.-

mitter.

Figure 4 illustrates a. to that of Figure'3'. V

vFigure'5 is a'circuit in which two pentodes are employed in push-pull as modulators in a slightly different Figure 6 "illustrates. a circuit in which the pentode is employed as the output valve of a transmitter.

Figure "Iillustrates .a modification of the cir cuit shown in Figure5. V

Referring to Figure lthe pentode I has its control grid circuit fedfrom the secondary of a transformer 2 whose primary is fed from the detector valve of the receiver-(not shown); The plate circuit. of said pentode l is supplied from a high tension battery3 'andincludes the primary of a transformer 4 whose secondary supplies the i The control of the auxiliary grid la is effected by means of an anode bend. detector 5 whose grid circuit is fed from the secondary of a trans-' former 6 the primary of which is supplied from the said detector valve of the receiver. The plate circuit of said anode bend detector .5 is also supplied from the same high tension battery 3 which supplies the plate circuit of the pentode I. but does not include the primary of the output transformer 4. wThe plate circuit 'of'the anode 'bend detector5 moreover'includes a resistance '1 which is not in the plate circuitzof the pentode. i, said resistance being connected between the high tension negative and theifilament of .said anode bend detector. said auxiliary grid vlct of Ithe pentode is connected to the filament of the anode-- bend detector 5 anda fixed condenser 8nis, ,c0n-- necte'd between:v said filament and the-remote side of; the, resistance. bend detector 5 isbi'ased by means'of grid biasv battery 9 so that when no speechcurrent'is ap-i plied to said grid no anode current fiowsin the The grid of: the anode plate circuit. Therefore no current will flow through the resistance ,1 .and the potential apwill be equal to the potential of the high tension negative. Hence the pentode I will be nontransmissive and the outputrcircuit therefrom will be dead. An incoming signal however affects the grid of the anode bend detector 5, causing current to flow in the plate circuit of the latter and therefore through the resistance I.

'A potential drop is therefore set up across this resistance .1 causing. its end remote. from the high tension negative to acquire a. posltive potential. This positive potential is applied'to the auxiliary grid Id of the pentode I and the same now becomes transmissive, amplifies the signals .and passes them freely to the output;

It has been found that in somecases the resistance I can be omitted without impairing the control of the pentode i I exercised by the anode bend detector 5. I Y r f Referring now to Figure 2 this shows an.,ar-

rangement similar to Figure 1 in which thegrid bias to the control grid of the pentode I is sup-. plied by the so-calledzautomatic methodby including a resistance In shunted by a condenser I I, in both the grid circuit and the plate circuit, between the filament of said 'pentode 'l and the point of junction of the hightensiongnegatil,

and the secondary of the transformer. In Fig-' ure 2 moreover a resistance I2 shunted by a condenser l3 has been connected between the con-. trol grid of the pentode -I and the secondaryof the transformer 2. This has the effect, of rendering the pentode l absoluteiy non-transmissive I 7 during the non-signal'periods even though the is I anode bend detector 5 transmits a'small anode j; current during these no-signal periods dueto the "the pentode, and, as the control. grid. ofthe pentode is being continuously energized by the input current, there will be a tendency for rectification to take place and. this will cause grid current to tend to flow. But uponthe firstap- "pearance 'of such grid. current the. control grid' will take up a negative potential with respecttothe filament dueto the potential drop in the resistance I0, and this will completely suppress the anode current rendering the valve absolutely.

non-transmissive.-

The-purpose of the condenser I 3 isthat of re- 1 ducing to a low value the impedance to the input signals during the periodf transmission,

and thereby maintaining efliciency during said period of transmission. x Z Referring now to Figure 3 the pentode l is employe'd ast'a modulator ina transmitter. In this:

case the auxiliary grid lais controlled bymeans of an anodebenddetector supplied in parallel from the same low frequency input transformer I4 as the pentode l; The control: in this case is eifectedin the same way asfin the preceding arrangements 'exceptithat allow pass: filteris connected in the line from theauxiliary grid la of'the'pentode l to the filament: of .the anodebend detector 5.

applied to the 'controlgrid of the'pentode 'Ifvary- This is to prevent the: voltage ing'instantaneously with the rectified currents of the anode bend detector 5. It willbe appre ciated that this filter which may consist-of'a choke l5 and condenser IE; will produce acertain time lag in the operation ofthe auxiliary grid Id of the pentode, but, by suitably choosing the values, a time constant of 1/50, to 1/200 of a second can be attained, which is a negligible quantity especially when speech is being transmitted. 1 V V The output from the pentode I is connected to the input of a large output valve I'I which is connected to the aerial circuit l8 in the usual way. l

The carrier wave frequency is supplied to the control grid circuit of the pentode I from a source I9.. Normally no carrier wave is transmitted, but

as soon as the signals to be transmitted are fed into the primary of the transformer I4 fully modulated' output radio signals are transmitted.

In the particular arrangement shown in the drawings the 'lowfrequency or modulating signals are supplied to the pentode I, from the seeondary.

.. of said transformer ,I 4, through an amplifier valvev 2G which is shown as being a pentode but might equally be atriode. In like manner these signals are supplied to'the anode-bend detector 5 through The reference 3a designates the high tension battery which is now connected" to the'anode bend detector only. The references and 23 designate plate circuit batteries-for the valves and 2| respectively; The valves 20 and 2! are provided with automatic grid biasing resistances 24 and, 25, whereas grid bias to the valves I and 5"is*provided by grid biasingba'tteries 26 and 21. Other details are deemed clear from the drawings.

The arrangement of Figure 4, which is highly suitablefor small transmitters, differs from that of Figure 3' ma number of respects. .Firstly the output valve I1 is dispensed with and the pentode I employed as output valve as well as modulator, the'primary'of an output transformer 28 being connected in the output circuit of sand pentode I. Also an oscillator valve" 29 is provided for driving said pentode I.

Further instead of the choke l5 of the low pass filter being connected, 'atits end'remote from the auxiliary grid -l'a,'to' the filament of the anode bend'detector 5, it is connected to a tapped point. of the grid bias battery 21 whichis negative with respect to saidfilament. The connection of the choke I5 to a point negative with-'respectfto' the filament may'belnecessary in certain casesfias I- have found, as heretofore stated, thatitis very acteristic of said valve, as this is the most sensitive point of its characteristic. A small current; thereforepasses through the resistance 1 in the anode circuit of 'siidanode bend detector 5 and due to this current a small v'oltagewou'ld normally be applied to the auxiliary grid Ia ofjthe pentode l,'but by connecting the choke l5 to a point which is negative with'respect-to the filament of the valve 5, that is with respect'to'the end of the resistance -1 remote from the high tension, this maybe compensated-for so that,'as before, no

potential is 'applied'to the auxiliary grid la of the pentodel when no signals are present. Figure '4 also differs fromFigure 3 in that, instead of the several high tens'ion'batteriesia, 22, 23, a common high tension battery 30 is employed for the valves 5, 20 and 2|. Other details such as the substitution of a resistance 3i for the grid bias battery ings.

Figure 5 illustrates an arrangement similar to Figures 3 and 4but in which two pentode valves l hav'e'their anodes connected incpush-pull. In this arrangement it will be seen that the amplifying valve' 2| of Figures 3 and 4 has been dispensed withiand'thatthe oscillator valve 29 is transformer coupled instead of resistance coupled. to the pentodes l. Otherwise, except that as stated the pentodes I and amplifiers 20 are in push-pull, the circuit of Fig. 5 is similar to those of Figures 3 and 4 and it is deemed that the operation will be clear from the drawings in view of the fact that like references are employed for corresponding parts in this Figure 5 as are employed in Figures 3 and 4.

"It may be remarked that, in this arrangement, since the control gridsof the pentode I are connected in parallel, if said pentodes were completely balanced there would be no carrier output 26 are deemed clear from'the'dr'awwhen there was no modulating input signal, even if the "auxiliary grid control in accordance with the present invention were not employed. Howeve'r;tin practice it is usually impossible to obtain valves which are completely balanced and a certain amount of carrier output would be normally transmitted if the auxiliary grid control were not employed.

Referring now to Figure 6 this shows a transmitteri'in'whichthe pentode valve 1 is employed as an output valve and is fed'from a triode high frequency amplifier valve 32 which acts as modulator. Thevalve 32 is fed with the low frequency modulating current from theltransformer l'4 through the medium of a triode valve 33- as shown which takes the-place of the pentode 20 of Figure 4, and is fed with unmodulated high frequency current from the source 19 as shown. The control of 'the' auxiliary grid l a is effected by means of the anode bend detector 5 in the same way as in Figure 3, a resistance l2 shunted by a condenser I3 being employed as in Figure 2 in order that complete quiescence shall be achieved during the no-signal periods. The anode bend detector is fed, from the transformer I4 through the amplifier 2| as in Figure 4, and this valve 2! has connected in the input circuit thereof a low pass filter consisting of inductances 34 and 35 and a condenser 36. This prevents any high frequency currents which may be fed back through the inter-electrode capacity of the valve 33 from being amplified by the valve 2| and fed to the valve 5. It will be appreciated that, if high frequency currents are fed to the valve 5, anode current will not be entirely suppressed during the no-signal period and therefore the pentode will not be entirely quiescent.

Figure 7 shows a similar arrangement to that of Figure 5, the two pentodes I being connected in push-'pull. This arrangement diifers from that of Figure 5 primarily in that the two valves l are fed from a single valve 20 instead of two valves 20 also connected in push-pull. A further minor difference is that the separate battery 3a for the plate circuit of the anode bend detector 5 is dispensed with, the battery 22 being employed for this purpose.

It will be clear to those skilled in the art that the invention is applicable to carrier wave telephony as well as radio.

It will also be clear that a lowpass filter could be employed in the case when the pentode is used as the output valve of a receiver, as well as, as

hereinbefore described, in the case when the pentode'is used as a modulator or. output valve of a transmitter. p v Y What I claim and desire to secure by Letters Patent is: 1'

- 1. In a modulating system, "a modulator tube having cathode, anode, control grid, and auxil iary grid, an input circuit connected betweensaid control grid and said cathode of said modulator tube, a rectifier tube having cathode, anode and grid and having its input circuit inel'ectric relation with theinput circuit of said modulator tube, an output circuit for said rectifier-tube comprising a resistor, an output circuit for said modulator tube, said output circuitshav'ing a common portion comprising a source of anode potential, and connections between the cathode" and auxiliary grid of said modulator tube and said resistor and said source of anode potential such that said source of anode potential applies to said auxiliary grid a negative potential with reference to the cathode of said modulator tube, and the voltage drop in said resistor due to' output current of said rectifier tube applies 'to said auxiliary grid a' positive potential with'reference to the cathode of said modulator tube.

2. Ina modulating system, a modulator tube havingcathode, anode, control grid, and auxiliary grid, an input circuit connected between said control grid and said cathode of said m'odulator tube, a rectifier tube havingcathode, anode and grid and having it input circuit in electric I relation with the input circuit of said modulator tube, aeommon source of anode potential for said tubes, having its negative terminal connected to the cathode of said modulatortube, and a resistor connected between the negative terminal of said source and the cathode of said rectifier tube, said auxiliary grid of said modulator tube being connected" to the cathode of said rectifier tube. v I

3. In a modulating system, a modulator tube having cathode, anode, control grid, and auxiliary grid, an input circuit connected between said'control grid and said cathode of said modulator tube, a rectifier tube having cathode, anode and grid and having its input circuit in electric relation with the input circuit of said modulator tube, an output circuit for said rectifier tube comprising a resistor, an output circuit for said modulator tube, said output circuits having a common portion comprising a source of anode potential, connections between the cathode and auxiliary grid of said modulator tube and said resistor and said source of anode potential such that said source of anode potential applies to said auxiliary grid a negative potential with reference to the cathode of said modulator tube,

and the voltage drop in said resistor due to output current of said rectifier tube applies to said auxiliary grid a positive potential with reference to the cathode of said modulator tube, and means for applying negative bias potential to the grid of said rectifier tube with reference to its oathode for substantially preventing the delivery of any output current therefrom when no input energy is applied to the input circuit of said rectifier tube.

4. In a modulating system, a modulator tube having cathode, anode, control grid and auxiliary grid, a modulator resistor having one terminal connected to the cathode of said modulator tube, an input circuit for said modulator tube connected between the terminal of said resistor remote from said cathode and saidcontrol grid, a rectifier tube having cathode, anode, and grid,

andhaving its input circuit in electrical relation with the input circuit of said modulator tube, a

common source of anode potential for said tubes having its negative terminal connectedfto said terminal of said modulator resistor remote from said cathode, and a rectifier resistor connected between the negative terminalof said source and the cathode of said rectifier tube, said auxiliary grid of said modulator tubebeing connected to the cathode of said rectifier tube.

5. In a modulating system, a modulatorltube havingcathode, anode, control grid, and auxiliary grid, an input circuit connected between said control grid and said cathode of said modulator tube, a rectifier tube of the anode-bend type 7 having cathode, anode and grid and having its input circuit in electric relationwith the input circuit of said modulator tube, an output circuit for said rectifier tube comprising'a resistor, an output circuit for said: modulator tube, said output; circuits having a common portion comprising alsourceiof anode potential, connectionsbetween the cathode and auxiliary grid of said modulator tube and said resistor and said source of anode potential such that said source of anode-poten tial applies to said auxiliary grid a negative potential with reference to the cathode of said modulator tube, and the voltage drop in said re-' 3 sistor due to output current of said rectifiertube applies to said auxiliary grid a positive potential with reference to the cathode of said modulator tube, and means for applying negative biaspotential to the grid of said rectifier tube with reference: to its cathode in such-manner that said' rectifier tube operates onits anode bend and substantially no output current is delivered there-V from when no input energy is applied to the input circuit of said rectifier tube. 1

6.11; a modulating system, a modulator tube having cathode, anode, control grid,and auxiliary circuit for said rectifier unit comprising aresistor,

and a circuit comprising a low-pass filter having a-time constant of the order of 1/ 50th .to 1/200th of a second connecting the terminals of said re-. sistor respectivelyto said-cathode and said au'xil-' iary grid ofsaid modulator tube in: such manner that the potential drop due to rectifier output current'opposes the potential appliedrto said auxiliary grid by said means, whereby the operation of said modulator tube is controlled through the portion of its input energy derived and applied through said rectifier unit. J a 7. In amodulating system, 'a-modulator tube having cathode,zanode, control grid, andauxiliar y grid, a source of sound-frequencylcurrent con nected totheinputcircuit of said modulator'tube',

a rectifiertube having cathode, anode, and grid,

and having itsinput circuit in-electrical' relation with the input circuit of said modulator tube,':an output circuit-for said rectifiertubecomprising a resistor, an output circuit for said modulator tube;

said output circuits having a commonportioncomprising a source of anode potential, afsource of rectifier grid bias potentialprovided with an intermediate'tap connected .for applying negative bias potential tothe grid of 'said rectifientube with reference to its cathode, anda circuit comprising a low-pass filter-delivering the potential between the negative terminal of said source :of

anode potential and said intermediate. tap across the cathode andauxiliary grid of said modulator LESLIE Hi PADDLE. 

